Axial flow gas turbine engines include a compression section, a combustion section and a turbine section. A flowpath for working medium gases extends through these sections of the engine. During operation, the gases are pressurized in the compression section and fuel is added in the combustion section. The fuel is burned to add energy to the pressurized gases. The hot, pressurized gases are expanded through the turbine section to provide the work of compression and hot, high pressure gases for subsequent use.
U.S. Pat. No. 3,898,799 issued to Pollert et al entitled "Device for Bleeding Off Compressor Air in Turbine Jet Engine" is an example of such a gas turbine engine. In Pollert, the compression section of the engine is provided with two independent mechanical compressors. During transient operating conditions, one compressor can provide more flow than can be accommodated by the second compressor. Accordingly, the compression section is provided with a plurality of passages extending about the working medium flowpath to allow a portion of the air to escape from the compression section. In particular, the engine has an inner ring that is provided with a plurality of openings. Each opening is covered or uncovered by an axially translating valve ring having radially extending seals. These seals extend radially between seal surfaces, as does a piston ring, between the valve ring and the circumferentially extending member having the openings. The valve ring is moved from an opened to a closed position by actuating means and includes guide rollers in one ring and guide slots in the other ring.
In other constructions, such as are found in some modern gas turbine engines, the engine is provided with circumferentially extending resilient seal members which extend axially between an axially translating valve ring and a seal surface. The valve ring is urged by simple actuating means from an open position to a closed position to axially compress the resilient seal members on either side of the openings to provide a gas tight seal.
As will be realized, the loss of working medium gases through the openings under steady state conditions when the compressors are operating at their design point will cause a decrease in the efficiency of the engine. Accordingly it is desirable to insure that flow does not occur through these openings under conditions which do not require the diversion of flow from the flowpath.
The above art notwithstanding, scientists and engineers working under the direction of Applicant's assignee have sought to decrease leakage through such seals by improving the sealing effectiveness of the seals and decreasing the effect that distortion resulting from operative load has on seal components.